The STOP key has two uses: as an emergency stop for the locos on the layout and as a shift key used in conjunction with other keys.
Emergency Stop key
The factory setting for the STOP key is for Local Emergency Stop which stops just the locos controlled by the two throttle knobs on the DT300. The STOP key can also be set for Global Emergency Stop which will stop all of the locos on the layout. This is done by setting throttle option switches.
Using the Stop key as a Shift Key
The STOP key is also used as a shift key in conjunction with other keys as described in other sections of this manual. When used as a shift key: press and hold the STOP key down (like the shift key on a keyboard) while pressing the second key. This will allow access to the alternative function of the second key. The STOP key is used as a shift key with the Y/+, N/- and FN/F0 keys.